At
dosages up to around 10 mg or so daily, selegiline retains its selectivity for the type-B
MAO iso-enzyme; but it is also a weak reversible inhibitor of the type-A MAO iso-enzyme.
In contrast to unselective and irreversible MAO inhibitors such as tranylcypromine
(Parnate) and phenelzine
(Nardil), both of which strongly potentiate the catecholamine-releasing effect
of tyramine, selegiline
inhibits it. This ensures that low-dosage selegiline does not induce the hypertensive "cheese
effect". A regimen of 2 x 5 mg daily of selegiline irreversibly inhibits over 90% of MAO-B in the basal ganglia, the location of over 80% of dopamine in the human brain. This level of MAO-B inhibition leads to a 40%-70% increase in synaptic dopamine.

Selegiline has immune-system-boosting
and anti-neurodegenerative effects. Its use increases the
level of tyrosine hydroxylase,
growth hormone, cerebral nitric oxide
and the production of key interleukins. Selegiline
offers protection against DNA damage and oxidative stress by hydroxyl and peroxyl
radical trapping; and against excitotoxic damage from glutamate.
In addition, selegiline stimulates the release of superoxide
dismutase (SOD). SOD is a key enzyme which helps to quench the production of damaging free-radicals. Potentially, selegiline may prevent or reverse iron-induced memory impairment. The deposition of excess iron in the brain is implicated several neurodegenerative diseases.

Selegiline protects the mitochondria via its effects on mitochondrial membrane permeability: it directly interacts with the pore-forming structures. Mitochondria are the energy powerhouses of the eukaryotic cell where oxygen respiration occurs. If the mitochondrial theory of aging is correct, then the root cause of aging is damage to mitochondrial DNA by free radical leakage from adjacent respiratory proteins. Alas selegiline itself is not an elixir of eternal youth. But its current "off-label" use by life-extensionists prefigures the longevity-enhancing mitochondrial medicine of decades to come.

Taken consistently at low
dosage, selegiline tends to extend the life-expectancy
of
rats by some 20%; enhances drive, libido
and endurance; and independently improves cognitive
performance in Alzheimer's patients and in some
healthy normals. Its protective role against age-related memory decline derives at least in part from its protection of hippocampal neurons in the aging brain. Aging drug-free rats have poorer spatial memories and fewer hippocampal neurons than their counterparts on selegiline. Selegiline is already used successfully to treat canine cognitive dysfunction
syndrome (CDS) in dogs.

Selegiline
retards the metabolism not just of dopamine but also of phenylethylamine,
a trace amine also found in chocolate
and released when we're in love.

Selegiline
protects the brain's dopamine cells from oxidative
stress. The brain has only about 30-40 thousand dopaminergic neurons in all. We
tend to lose perhaps 13% a decade in adult life. An eventual 70%-80% loss leads
to the dopamine-deficiency disorder Parkinson's
disease, frequently foreshadowed by depression. Selegiline in pill form was approved by the FDA as an adjunct in the treatment of Parkinson's disease in 1989. In June 2006, the FDA approved once-daily orally disintegrating tablets of selegiline HCl branded as Zelapar from Valeant Pharmaceuticals. Zelapar is used as an adjunct therapy for Parkinsonians on levodopa/carbidopa (Sinemet) whose response is deteriorating. The cocktail allegedly reduces "off" time by an average of 2.2 hours per day.

Administered at low
doses, selegiline is neuroprotective
against possible damage to the serotonergic fine axon terminals caused by overconsumption
of the popular drug MDMA (Ecstasy). Several
competing theories exist that purport to
explain MDMA-induced neurotoxicity. One theory blames the deamination by MAO-B
of excessive dopamine taken up by the membrane-bound
transporter into the depleted serotonin terminals. This abnormal uptake
follows MDMA-induced reversal of the serotonin reuptake pump. In the absence of
MAO-B inhibition, deamination by MAO-B of excess dopamine taken up into the serotonergic
axon terminals is liable to generate a glut of toxic free radicals. These highly
reactive compounds cause membrane lipid peroxidation and consequent fine terminal
degeneration. Selegiline prevents such serotonergic damage, in theory at any rate.

On the other hand, co-administering
unselective selegiline dosages or unselective irreversible MAOIs like tranylcypromine
(Parnate) or phenelzine
(Nardil) with MDMA is potentially lethal.

Taken at MAO-B-selective dosages,
selegiline is typically less effective as a mood-brightener than other dopaminergics
such as amineptine (Survector) - though occasionally spectacular remission of depressive symptoms may occur even with minimal MAO-A inhibition. Taken at
unselective dosages of 20mg a day or more, selegiline is typically an effective,
well-tolerated antidepressant. Selegiline at higher dosages may also be useful
for "atypical" depressive symptoms of overeating, oversleeping,
and hypersensitivity to rejection. An unselective dosage regimen would normally call for an MAOI
diet (no cheese, red wine, fava beans, salami, etc).

Wrangling over labelling issues delayed EMSAM's product launch. But in February 2006, the FDA granted EMSAM a product license for the treatment of major depressive disorder in adults. EMSAM's pharmacokinetic and pharmacodynamic properties promote the inhibition of MAO-A and MAO-B in the CNS while avoiding significant inhibition of intestinal and liver MAO-A enzyme.

Three different strengths of EMSAM patch are currently marketed: 20mg/20cm2, 30mg/30cm2, and 40mg/40cm2. The three patch sizes deliver daily doses of selegiline averaging 6mg, 9mg and 12mg respectively. Use of the lowest dosage EMSAM 6 mg/24 hour patch doesn't call for dietary modification. Certainly at the lower dosage range, MAO-A in the digestive tract is preserved at levels more than adequate to break down tyramine, while MAO in the brain is inhibited at levels adequate to induce an antidepressant effect. A restricted "MAOI diet" is prudently advised for the higher dosage EMSAM 9 mg/24 hr patch and the 12 mg/24 hr patch to avoid any risk of hypertensive crisis. But it's worth noting that (as of 2008) no hypertensive crises following dietary indiscretions have been reported even in users of the high strength patches.

Other prescribing indications for selegiline are in prospect. In November 2004, Yale University researchers launched a study of selegiline for smokers who want to quit tobacco.

Unlike selegiline, the novel irreversible selective MAO-B-inhibitor rasagiline (Azilect) is not metabolised to methamphetamine or amphetamine. These trace amines are unlikely to contribute to selegiline's neuroprotective action. Azilect has been licensed in the EC from mid-2005; but labelling disputes with the FDA delayed the product launch of rasagiline/Azilect in the USA until May 2006.

Either
way, by the standards of posterity we are all little better than glorified glue-sniffers in the light of the chemicals we put into our bodies.
The impending Post-Darwinian Transition
to an era of paradise-engineering
has dreadfully crude origins. But by today's modest standards, at least, selegiline is
a potentially life-enriching agent...."